POTENTIAL CASE OF INDUCED SEISMICITY FROM A WATER DISPOSAL WELL IN SOUTH-CENTRAL OKLAHOMA

On September 17, 2013, a swarm of earthquakes began in Love County, Oklahoma, north of Marietta. These earthquakes began occurring about two weeks after injection began at a nearby disposal well. The largest earthquake was a magnitude 3.4, which did minor damage to structures in the epicentral area and had a maximum Modified Mercalli Intensity of VII. Local residents consistently feel magnitude 1.8 earthquakes. The earthquakes are occurring at shallow depths consistent with injection depths of the nearby disposal well. The sequence included 22 earthquakes of magnitude 2.0 or greater with more than 100 earthquakes identified during the period which injection occurred. Regional seismic stations provide poor coverage of the earthquakes, in part due to the shallow focal depths. A temporary network of six seismic stations was deployed in the area. This network greatly enhanced earthquake locations and dramatically improved the magnitude of completeness. Earthquakes continued after injection ceased but at a lower frequency and smaller magnitudes with only one felt earthquake. This area has seen similar shallow earthquake swarms in the past. It is important to address whether or not this swarm of earthquakes is caused by fluid injection at the nearby disposal or simply an unlikely coincidence. Techniques used to improve event identification and locations of the earthquakes are presented. A statistical method to quantitatively address seismicity changes is adopted and implemented in a monitoring system, in the event injection resumes in the disposal well or in a nearby well that was recently completed. The operator of the disposal well is currently restricted on injection rates and volumes, but may continue injection under the yellow light condition placed on injection by the Oklahoma Corporation Commission. However, the operator has not currently chosen to inject under these restrictions, if injection resumes the results of the statistical monitoring and traffic light system will be presented.